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Alternator got SMOKING HOT

Florin1
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Florin1

Florin1

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Hey all. I bought my truck as a theft recovery, and so all the battery wires were cut up. I replaced the wires, and also the serpentine belt this evening due to a failing damper. I fired it up and let it idle, everything looked fine, and then like 5 min of idling and I started smelling an almost burnt plastic smell. Was looking at the alternator and could see smoke, so I killed the engine. The alternator was extremely hot! It looked like some of the solder or whatever holds the copper wires together, started boiling. Looked like tar. I wasn’t sure if it was motor oil that got splashed onto the alternator. Not sure. B it the smell was definitely not oil, and it definitely stunk! The alternator didn’t make any noise either. I thought that maybe I routed the serpentine belt wrong, but I triple checked, and it’s as per the sticker on radiator support. I took tension off the belt with the idler, and spun the alt. pulled in both directions and it spun freely. And there wasn’t any play in it either. Any ideas? Thank you. 
 

2001 Cummins 2500 4x4 5speed. 

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Haggar

Haggar

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Full fielding was a diagnostic in the old days when regulators were separate from alternators (or other computer components...)

To diagnose if your issue was voltage regulation or alternator (or generator....) you needed to separate the two.  By full fielding the alternator, you would command it to put out full voltage and amperage output.  if you didn't get like 16v (at idle) and it starting to get warm (from making amps) you knew the alternator was bad.  If it did produce the voltage and heat up, you knew your regulator was bad.

 

HTH

 

Hag

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Florin1

Florin1

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Hmm ok. Here is something I found, that now I’m thinking is possibly related? 
don’t see how to post pictures off my phone so I’ll describe.

under the hood fuse box, there’s two fat wires on the onboard side of fuse box. They are bolted down and bridged together by some kind of “fuse”. That fuse is broken now. 

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Mopar1973Man

Mopar1973Man

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Alternator is shot, diodes shorted out. You'll need to pull the alternator and test it and replaced. Then you'll need to replace the fuse.

 

Done properly you should do the W-T ground wire mod and the PCM protection fuse. Like mine when it failed it wiped out my PCM and the alternator was about 400*F when it failed. Cost me an alternator and $800 PCM replacement. 

 

 

 

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JAG1

JAG1

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My alternator got smokin hot and turned out to be a dead cell in one of the batteries. Be sure to load test the batteries separate as a bad cell can put the alternator into full on and cook itself trying to feed that bottomless pit. Soon as I put in new batteries the problem went away.

 

Additionally, W-t ground mods one of the best things for these trucks.

Edited by JAG1
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Mopar1973Man

Mopar1973Man

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10 minutes ago, JAG1 said:

My alternator got smokin hot and turned out to be a dead cell in one of the batteries. Be sure to load test the batteries separate as a bad cell can put the alternator into full on and cook itself trying to feed that bottomless pit. Soon as I put in new batteries the problem went away.

 

Being a bad cell is a permanent short. This short continues to bleed amperage, turning into heat in the battery or batteries if both have issues then the constant load will increase on the alternator load only to create heat in a bad battery. Bigger alternator will not fix this problem but remove the parasitic load of the bad cells and the heat and alternator problem will go away.   

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Tractorman

Tractorman

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@Florin1, could you make a couple of clarifications?

 

1 hour ago, Florin1 said:

I just put new/refurb batteries in it. From interstate batteries.

 

Are these new batteries? Or, refurbished batteries?  Before replacing the alternator, I would disconnect all battery cables and check battery voltage independently.  The battery voltage will probably be around 12.5 volts because the alternator has not been charging the batteries. They should be within one tenth of a volt (.1 volts) of each other (this is important).  I would leave the batteries disconnected and then recheck voltage independently about 24 hours later.  The results should be the same.  If one battery voltage is significantly lower than the other battery, then both batteries should be replaced.

 

2 hours ago, Florin1 said:

under the hood fuse box, there’s two fat wires on the onboard side of fuse box. They are bolted down and bridged together by some kind of “fuse”. That fuse is broken now. 

 

Is this fuse broken?   Or, is this fuse blown?  If that 145 amp fuse (alternator output) is broken, that could explain the alternator getting hot quickly as the PCM would sense low battery voltage all the time and would command maximum continuous output from the alternator.  If this fuse is blown, then you will need to figure out why the fuse is blown.

 

In either case, fully charged known good batteries should be installed.  To protect the new alternator, I would do the following: 

 

Disconnect grid heaters at battery (driver's side)

Replace the 145 amp alternator output fuse.  

Install the new alternator and connect the field wire connector.  Do not connect alternator output wire at this time. 

Reconnect both batteries

Fabricate a 5 amp fuse temporary jumper wire.

 

Before starting the engine, install the temporary jumper wire with 5 amp fuse  - one end to the alternator output terminal and the other end to the alternator output wire.   If the temporary fuse does blow, then you need to find out why before proceeding further.

 

If the fuse does not blow, you can connect the alternator output wire to the alternator and start the engine.  Have a multimeter handy and check battery voltage immediately.  Battery voltage should rise to about 14 volts and become steady.  If battery voltage continues to rise (does not stabilize), shut the engine off immediately.  Further diagnostics will be necessary. 

 

I would personally follow this procedure so I wouldn't destroy a new alternator.

 

- John

 

 

 

 

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Florin1

Florin1

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21 hours ago, Tractorman said:

@Florin1, could you make a couple of clarifications?

 

 

Are these new batteries? Or, refurbished batteries?  Before replacing the alternator, I would disconnect all battery cables and check battery voltage independently.  The battery voltage will probably be around 12.5 volts because the alternator has not been charging the batteries. They should be within one tenth of a volt (.1 volts) of each other (this is important).  I would leave the batteries disconnected and then recheck voltage independently about 24 hours later.  The results should be the same.  If one battery voltage is significantly lower than the other battery, then both batteries should be replaced.

 

 

Is this fuse broken?   Or, is this fuse blown?  If that 145 amp fuse (alternator output) is broken, that could explain the alternator getting hot quickly as the PCM would sense low battery voltage all the time and would command maximum continuous output from the alternator.  If this fuse is blown, then you will need to figure out why the fuse is blown.

 

In either case, fully charged known good batteries should be installed.  To protect the new alternator, I would do the following: 

 

Disconnect grid heaters at battery (driver's side)

Replace the 145 amp alternator output fuse.  

Install the new alternator and connect the field wire connector.  Do not connect alternator output wire at this time. 

Reconnect both batteries

Fabricate a 5 amp fuse temporary jumper wire.

 

Before starting the engine, install the temporary jumper wire with 5 amp fuse  - one end to the alternator output terminal and the other end to the alternator output wire.   If the temporary fuse does blow, then you need to find out why before proceeding further.

 

If the fuse does not blow, you can connect the alternator output wire to the alternator and start the engine.  Have a multimeter handy and check battery voltage immediately.  Battery voltage should rise to about 14 volts and become steady.  If battery voltage continues to rise (does not stabilize), shut the engine off immediately.  Further diagnostics will be necessary. 

 

I would personally follow this procedure so I wouldn't destroy a new alternator.

 

- John

 

 

 

 

Thank you gentlemen for the wonderful tips. I will hopefully get out to the truck today and apply what you’ve all said. I tried to reply back yesterday, but I reached my “maximum posts for the day”. I was surprised to see this. I’ve donated in the past, didn’t realize rules have changed. 
 

John, 

the batteries are refurbished from interstate batteries. Like I just bought them a couple weeks ago from them. The 145A fuse was blown. I’m embarrassed to say, but I actually put a dab of solder on the break to make the connection again thinking surly my tiny solder bridge was thinner than original fuse. This was the first thing I did when I got the truck. Didn’t occur to me that that’s why the alternator got hot. Also I don’t have the fuse box cover so I didn’t even know what that fuse was to. I assumed it blew because when the truck got stolen, and they cut out the batteries and cables, they shorted something out. Still may be the case.  I guess this would explain the alternator/generator getting so hot? 
 

I found a guy locally parting out a 1999 cummins and he will sell me his alternator for $30. So I’ll be picking that up on Saturday. 
 

 

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Tractorman

Tractorman

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1 hour ago, Florin1 said:

I guess this would explain the alternator/generator getting so hot? 

 

Yes, this could be a possible explanation.

 

22 hours ago, Tractorman said:

Before starting the engine, install the temporary jumper wire with 5 amp fuse  - one end to the alternator output terminal and the other end to the alternator output wire

 

One more thing to add to this step. After connecting the temporary jumper wire with a 5 amp fuse, use a test light to check for battery power at the alternator output terminal (via the 145 amp fuse).  Do this before starting the engine.  The test light should illuminate brightly.  If the test light does not illuminate at all, or illuminates dimly, do not start the engine.  There should be unrestricted continuity from the alternator output to the 145 amp fuse.

 

I think you will get this figured out - just be cautious along the way.  No telling what is wrong with a stolen vehicle with cut wires.

 

- John

Edited by Tractorman
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Mopar1973Man

Mopar1973Man

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22 hours ago, Florin1 said:

I’ve donated in the past, didn’t realize rules have changed. 

 

We had too. Being than less than 1% were donating and wasn't fair. more than 99% were riding on others for free. Now everyone pitches in a small amount making it fair for everyone. 

 

22 hours ago, Florin1 said:

The 145A fuse was blown.

 

This means the diodes in the alternator are failing. People think the fuse is for a run away alternator and stops the alternator from runaway conditions of overcharging. Actually the fuse is too big for stock alternator to blow even at 100% field and loading of 195 amps of grid heaters. When the fuse blows this test me the diode(s) have shorted to ground and blown the fuse. I would highly suggest taking the alternator off and having it benched for AC noise issues. The 145A fuse was blown.

 

22 hours ago, Florin1 said:

 I guess this would explain the alternator/generator getting so hot? 

Again the diodes are shorting out causing the heat issue. Heat is a sign of high current going where it should not go typically finding a path to ground. 

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Florin1

Florin1

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Update: 

I bought a used alternator and a 140A fuse off a  99 cummins somebody local is parting out. Went home and tried to follow John’s great tips. Both batteries were reading 12.5 volts. I put the 140A fuse on,  I took off old alternator, and put new one in. Made a 5A jumper fuse between the B+ wire and the stud on alternator. Disconnected the grid heater wire at the positive driver battery post. It wasn’t clear if you wanted me to start the truck next, or just key on to see if the fuse 5A fuse popped. So I just did key on, and it didn’t pop. So I hooked up the B+ and started truck. I put my volt meter on the battery posts and it was reading steady at 14.33v on both batteries. And 14.35 at alternator I think. I let it idle for 5 min, and voltage stayed steady at 14.33. So does this mean PROBLEM SOLVED? :)

I am thankful for your help guys. 
 

MM, where do I chip in? 

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